The present invention relates to semiconductor device fabrication and integrated circuits and, more specifically, to structures for a field-effect transistor and methods of forming a field-effect transistor.
Device structures for a field-effect transistor generally include a body region, a source and a drain defined in the body region, and a gate structure configured to apply a control voltage that switches carrier flow in a channel formed in the body region. When a control voltage that is greater than a designated threshold voltage is applied, carrier flow occurs in the channel between the source and drain to produce a device output current.
Epitaxial semiconductor films may be used to modify the performance of field-effect transistors. For example, an epitaxial semiconductor film can be used to increase the carrier mobility by inducing stresses in the channel. In a p-channel field-effect transistor, hole mobility can be enhanced by applying a compressive stress to the channel. The compressive stress may be applied by forming an epitaxial semiconductor material, such as silicon-germanium, at the opposite sides of the channel. Similarly, in an n-channel field-effect transistor, electron mobility can be enhanced by applying a tensile stress to the channel. The tensile stress may be applied by forming an epitaxial semiconductor material, such as silicon doped with carbon, at the opposite sides of the channel. These stressors may also operate as portions of source and drain regions of the field-effect transistor, and may function as a dopant supply for other portions of the source and drain regions.
The volume of the epitaxial semiconductor material contained in the stressors may be directly linked to device performance and yield. The stress imparted to the channel increases with increasing volume, which optimizes mobility. Increasing the volume may also reduce the source and drain resistance, and may also provide a consistent contact landing area in certain situations.
Accordingly, improved structures for a field-effect transistor and methods of forming a field-effect transistor are needed.